Differential Induction of 3-Hydroxy-3-methylglutaryl CoA Reductase in Two Cotton Species Following Inoculation with Verticillium. Oscar Joost . Department of Plant Pathology and Microbiology, Texas A&M University College Station 77843. Graciela Bianchini (2), Alois A. Bell (3), C. R. Benedict (2), and Clint W. Magill (1). (1) Department of Plant Pathology and Microbiology, Texas A&M University College Station 77843, (2) Department of Biochemistry and Biophysics, Texas A&M University, College Station 77843, (3) USDA, ARS, Southern Crops Research Laboratory, College Station 77845, U.S.A. MPMI 8:880-885. Accepted 9 August 1995. Copyright 1995 The American Phytopathological Society.

Gossypium barbadense cottons are typically more resistant to wilt pathogens than are Gossypium hirsulum cultivars. Both species make terpenoid phytoalexins in response to infection, implicating isoprenoid biosynthesis as a factor in resistance. Conserved regions in plant 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), the first enzyme in the terpene biosynthesis pathway, were used to design polymerase chain reaction primers for cloning a fragment of a cotton HMGR gene. The clone was used as a probe on Northern blots to show that induction of HMGR mRNA following introduction of Verticillium dahliae spores into the vascular system is much more rapid in Seabrook Sea Island, a resistant G. barbadense cotton, than it is in Rowden, a susceptible G. hirsutum. The amount of HMGR mRNA returned to near control levels in 4 days in the former variety but continued to accumulate in the latter. Specific enzyme activity of HMGR also increased more rapidly in stele extracts of Seabrook Sea Island than in Rowden.